Inert dental glass

ABSTRACT

The invention relates to the use of ions of weakly basic oxides as linking ions for polyacids in cements, preferably polyelectrolyte cements. Suitable ions comprise elements of the scandium series, for example, Sc 3+ , Y 3+ , La 3+ , Ce 4+  and all subsequent tri- and tetra-valent lanthanides and the ions Mg 2+ , Zn 2+ , Ga 2+ , In 2+ . The application of said ions permits a regulation of the cement reaction without surface treatment of the glass powder.

This application claims the priority of International Application No.PCT/EP01/14721, filed Dec. 13, 2001 and German Application No. 100 63939.9, filed Dec. 20, 2000, the disclosures of which are expresslyincorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to the use of unreactive glasses in dentalmaterials, in particular dental cements, preferably polyelectrolytecements, which can be used without pretreatment of the glass powdersurface.

In the dental sector, glasses are used in particular for fillingmaterials and for the fixing cements and composites for crowns, bridgesand inlays.

Reactive glasses, i.e. glasses which participate in a chemical reaction,are used in what are known as polyelectrolyte cements, in particularglass-ionomer cements.

Polyelectrolyte cements of this type generally comprise threeconstituents, namely a polyacid, in particular a substance whichcontains carbonic acid, preferably in liquid form, a glass powder andwater. If the three components are combined and mixed with one another,a reaction occurs, so as to form a solid body which hardens over thecourse of time (cement reaction).

Various raw materials are used for the production of glasses which areused in particular in glass-ionomer cements. These raw materials arefirstly oxides, such as SiO₂, Al₂O₃, CaO, fluorides, such as CaF₂, SrF₂,cryolite, hydroxides, such as Al(OH)₃, phosphates, such as AlPO₄, P₂O₅or calcium phosphates. However, it is also possible to use silicates,such as mullite, or carbonates, such as Na₂CO₃, CaCO₃ or other naturalmineral raw materials. In principle, it is also possible for all the rawmaterials to be used in a form which contains water of crystallization.

In dental glasses, a considerable proportion of the oxygen is oftenreplaced by fluorine. This is indicated by adding the element symbol Ffor fluorine to the description of the glass system.

Accordingly, glasses for glass-ionomer cements can usually be assignedto one of the following systems, in which P₂O₅ and Na₂O in some casesare only present in small amounts or are not present at all:SiO₂—Al₂O₃—CaO—(P₂O₅)—(Na₂O)—FSiO₂—Al₂O₃—SrO—(P₂O₅)—(Na₂O)—FSiO₂—Al₂O₃—SrO—La₂O₃—(P₂O₅)—(Na₂O)—FSiO₂—Al₂O₃—CaO—La₂O₃—(P₂O₅)—(Na₂O)—F

The glasses which are used in dental cements are generallyfluoroaluminosilicate glasses. The solubility of the glass in acid is aprecondition for it to be used as a constituent of a polyelectrolytecement. An acid-soluble glass structure is formed if silicon ispartially replaced by aluminum. However, silicon can only be replaced byaluminum if basic oxides are present, in order to create chargeequalization for the trivalent aluminum ion at positions of thetetravalent silicon ion.

When the polyacids and water are added, the glass structure is brokenup, and in particular the ions with network-modifying properties are atleast partially released as what are known as crosslinker ions.

The crosslinking manifests itself in hardening of the cement whichincreases over the course of time. All at least divalent basic ions, butalso Al³⁺, are able to form polymeric structures of this type.

A distinction is usually drawn between the working time—the time duringwhich the dentist is still able to work the still pasty cementmaterial—and the hardening time—the time beyond which reworking ispossible using rotating dental instruments.

It has been found that conventional glasses, which contain, for example,Ca²⁺ and Al³⁺ as crosslinker ions, in untreated form are too reactiveand, on account of an excessive solubility, set too quickly with thepolyacid, and consequently the dental cement which forms cannotreasonably be worked.

Although it is possible to slow the dissolution process by reducing thecalcium content in the glass, it has been found that if the level ofbasic oxides, such as CaO or SrO, which can dissolve, is too low, thestrength properties of the cement deteriorate as a result ofinsufficient availability of the ions. This means that the dentist hasonly a very short working time available to mix the filling material andapply it. At the same time, he has to accept the drawback of having towait a very long time before he can start reworking the cement. Thisruns contrary to the demands which a dentist will impose on a dentalcement.

The dentist usually requires a working time of from 1 to 4 min and ahardening time of from 5 to 8 min. The hardening time is usuallydetermined according to ISO 9917 (First Edition) Part 7.3. The workingtime and the hardening time can be determined using a viscometer, asdescribed in EP 0 023 013 A.

To achieve the desired working properties of the cement, i.e. to havesufficient working time and the shortest possible time to completehardening, it is customary for the glass powders, after the millingprocess, to be subjected to surface treatment, as described, forexample, in Clinical Materials 12, 113–115 (1993) or DE 29 29 121 A (EP0 230 113 A). In this case, the glasses which react too quickly, onaccount of their composition, are adjusted to the desired level ofreaction rate by reducing the levels of reactive ions at their surface.

EP 0 023 013 A describes the use of a calcium aluminum fluorosilicateglass powder for glass-ionomer cements to which further oxides may beadded if they do not adversely affect the properties of the glass.According to the description, the surface of the glass has to bedeactivated in order to obtain a glass which can be used for a dentalcement. The deactivation represents a procedure whereby the reactionrate of a glass powder with an acid is delayed by a surface treatment,and in this way the desired working times of the cement are produced.

The deactivation of the surface can also be effected by means of other,relatively complex surface treatments, such as coating the surface, forexample with a polymer.

In EP 0 023 013 A, this is achieved by means of a chemical treatment ofthe powder surface. The result is a cement with favorable working timescombined, at the same time, with unchanged favorable mechanicalcharacteristic data of the material.

However, this surface treatment of the glasses represents a complexprocess step.

Moreover, during the washing or conditioning processes, powderagglomeration may occur, having an adverse effect on the cementproperties.

DE 38 06 448 A has disclosed a glass for a bone cement which comprisesthe elements Si, Al, Ca, Sr, F, Na and P and can be made visible toX-rays by the addition of La₂O₃. It is emphasized that the quantity ofadditives must not adversely affect the properties.

The glass powder described in DE 38 04 469 A is substantially free ofalkali metal ions and alkaline-earth metal ions, with the exception ofstrontium which should be used in an amount from 15 to 40% by weight.

DE 20 65 824 B2 has described a fluoroaluminosilicate glass powder forself-hardening medical cements.

One object of the present invention is to provide a glass for a dentalcement, in particular a reactive glass for a polyelectrolyte cement,which is simple to produce.

A further object can be considered to lie in that of directly using theglass immediately after the milling process without having to applycomplex processes such as surface treatment, acid washing, coatingand/or conditioning. The reactivity and therefore the working time andhardening time are then dependent only on the glass composition and thegrain size distribution and are easy to produce reproducibly.

This object is achieved by a dental material containing a glass asdescribed in the claims, and by the use of certain ions as crosslinkerions in a glass.

The invention also relates to hardenable materials, in particularcements, in particular polyelectrolyte cements, which contain theseglasses.

In one embodiment, the invention relates to a process for producing adental glass involving the steps a) providing oxidic substances, b)mixing the oxidic substances, c) melting the mixture from step b), d)quenching the molten material to form a solid, e) milling the solid fromstep d) to form a glass powder, the glass powder from step d) not beingtreated with acid before it is used in a dental cement.

In the context of the present invention, the term crosslinking is to beunderstood as meaning a reaction in which polyacids and at leastdivalent ions interact with one another in a chelate-forming reaction,preferably an acid-base-type reaction, leading to the formation of apolymeric network.

In the context of the present invention, the filling and fixingmaterials mentioned are to be understood as meaning substantiallycements, and in particular polyelectrolyte cements. Accordingly, theglass described is preferably a reactive constituent rather than aconventional filler, unlike the glasses used in the composite sector,which are pure fillers and do not take part in a reaction.

Glasses for cements generally contain strongly basic ions, such as Li²⁺,Na²⁺, K⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺. It has now been found that bycompletely or partially replacing the strongly basic ions with weaklybasic ions, such as Sc³⁺, Y³⁺, La³⁺, such as Ce^(3+/4+) or otherdivalent, trivalent or tetravalent ions from the lanthanide series,and/or Ga²⁺ or In²⁺, glasses which set significantly more slowly withpolyacids are obtained.

Surprisingly, such glasses can be used to produce dental cements which,substantially without a conventional surface treatment of the glasspowders, have setting characteristics which are desired by the dentist.Furthermore, it has been found that the setting times can be adjustedwithin a wide range by means of the glass composition.

In this context, the invention has the following advantages:

As a result of the strongly basic ions, such as Ca²⁺, Sr²⁺, beingreplaced by the weakly basic ions Sc³⁺, Y³⁺, La³⁺, Ce^(4+/3+) and otherdivalent, trivalent and tetravalent ions from the lanthanide series inglasses which are used in dental cements, it is possible to achieve acontrolled setting reaction of the dental cement, in particular of aglass-ionomer cement, without the glass having to be surface-treated,for example by acid washing and/or conditioning, before being used inthe cement. In addition to simplified production, the advantage alsoresides in the improved reproducibility of the working and hardeningtimes. Although these times are not adjusted by a surface treatment, thedesired setting profile, namely a relatively rapid transition from astate in which the cement can still be worked to a state in which thehardening begins and useful working is no longer possible, issurprisingly achieved.

Amazingly, it has been discovered that dental materials or cement inwhich the abovementioned glasses are used have mechanical propertieswhich are identical or even slightly improved compared to cements inwhich glasses whose reactivity has been reduced by acid washing areused.

Furthermore, it has been found that cements according to the inventionare hydrolytically stable with respect to water.

These properties were found in particular in glasses which, in additionto Al and Si, contain only Y and/or La or contain only relatively smallamounts of relatively strongly basic-reacting ions, such as Ca²⁺ orSr²⁺, Ba²+, Li⁺, Na⁺, K⁺.

Furthermore, some of the oxygen can be replaced by fluorine, which onthe one hand improves the meltability of the glass and on the other handimproves the setting properties of the cement and makes it possible torelease fluoride ions for secondary caries prophylaxis.

Therefore, the previously known cement systems are expanded by theaddition of the following systems.SiO₂—Al₂O₃—(SrO)—Ln_(x)O_(y)—P₂O₅— (Na₂O)—FSiO₂—Al₂O₃—(CaO)—Ln_(x)O_(y)—P₂O₅— (Na₂O)—F

Ln_(x)O_(y) stands for an oxide of the elements Sc, Y, La to Lu. x and ymay adopt values of 1, 2 or 3 in this formula. The oxides which areinside parenthesis are used in only small amounts or are not used atall, since they would greatly accelerate the reaction. For example, DE20 65 824 A describes a glass belonging to the systemSiO₂—Al₂O₃—La₂O₃—P₂O₅—Na₂O—Fhaving an Na₂O content of approx. 12% by weight.

Tests have shown that with this glass powder the setting rate withpolyacids can only be brought into a manageable range after conditioningfor several hours at 400° C. (cf. Comparative Example 4). This ispresumably attributable to the high level of a strongly basic oxide, inthis case Na₂O. A further drawback of a high Na₂O content is theincreased water solubility of the resulting cement.

Moreover, it has been found that the glasses described substantially donot have any phase-separation or crystallization effect within a widerange of compositions.

It is to be expected that the reproducibility of the setting rate of thecement containing the glasses will improve with clear glasses comparedto segregated, i.e. opaque glasses, since their phase composition is notdependent on the cooling rate.

In addition to the standard components SiO₂, Al₂O₃, P₂O₅, and Na₂O, theglasses preferably mainly contain weakly basic and/oramphoteric-reacting ions, which act as crosslinker ions during thecement reaction.

Weakly basic trivalent and tetravalent ions are preferred, and the ionsSc³⁺, Y³⁺, La³⁺, Ce^(4+/3+) and all the following trivalent andtetravalent ions from the lanthanide series are particularly preferred.

Current teaching is that Al³⁺ also belongs to the weakly basic oramphoteric-reacting ions. However, this ion adopts a special positionamong the glasses. Aluminum is primarily responsible for the solubilityof the glass structure in acid and has only a secondary function as acrosslinker ion. In the glasses which are suitable for dental cements,aluminum, unlike the abovementioned trivalent and tetravalent ions,which function as network modifiers, acts as a network former.

The glasses used generally have a BET surface area of from 1 to 15 m²/g,preferably 2 to 8 m²/g.

Furthermore, the glasses have a mean grain size (d₅₀) of from 0.01 to 20μm, preferably 1 to 5 μm.

It is preferable for 0 to 25% by weight of the oxygen in the glass usedto be replaced by fluorine, particularly preferably from 8 to 18% byweight.

The pK_(B) value is usually used to define the term basicity. A pK_(B)of one can be taken as the limit between weakly and strongly basic. Forexample, the pK_(B) of Mg(OH)₂ is given as one in R. C. Weast: CRCHandbook of Chemistry and Physics, while Ca(OH)₂ is classified asstrongly basic, without being assigned a numerical value.

In the context of the present invention, oxides or hydroxides which onlydissociate to a relatively minor extent in aqueous solutions areconsidered to be weakly basic.

In one embodiment, oxides with a pK_(B) value of >1 are provided.

The following statements can be made in connection with the basicity:

The basicity increases from Sc through Y to La. La is to be classifiedas weakly basic compared to Sr, Ba or Na and K. At the same time, thebasicity decreases again from La to Lu, and consequently the basicity oflutetium is approximately comparable to that of yttrium (lanthanidecontraction).

Therefore, all oxides and hydroxides of the Sc series can be consideredweakly basic in the context of present invention.

The elements from the 1st main group from Li through Cs and the elementsfrom the second main group from Mg through Ba cannot be classified asweakly basic-reacting in the context of the present invention.

As has already been stated, it is assumed that, in addition to the basestrength, the higher field strength of these ions also plays a certainrole. This means that the ions described are anchored more strongly inthe glass structure and are therefore dissolved out of it more slowly.

In the context of the present invention, the term polyacid is understoodto mean a polyelectrolyte which includes a polymer with ionicallydissociable groups, which may be substituents in the polymer chain andthe number of which is so great that the polymers, at least in their(partially) dissociated form, are at least partially water-soluble.Substituents such as for example —COOH, —OH, —PO(OH)₂, —OPO(OH)₂,—SO₂(OH) are particularly suitable for this purpose. Organic polyacids(DE 20 61 513 A), such as polymers and copolymers of acrylic acid,methacrylic acid (EP 0 024 056 A), itaconic acid, maleic acid,citraconic acid, vinylphosphonic acid (EP 0 340 016 A; GB 22 91 060 A)are particularly preferred. In addition, if a plurality ofpolyelectrolytes are present, water-insoluble polyelectrolytes may alsobe present in the polyelectrolyte cement. The only condition is that atleast one of the polyelectroytes be at least partially water-soluble.

The polyelectrolytes should be able to react with the glass component aspart of a chelate-forming reaction and/or an acid-basereaction/neutralization reaction.

The polyelectrolyte cement contains the at least partially water-solublepolyelectrolyte, which can be converted into the solid state, preferablyin an amount from 0.5 to 30% by weight, particularly preferably 2 to 25%by weight and very particularly preferably 5 to 20% by weight.

In the case of polyelectrolyte cements, the addition of chelating agentsin order to establish a suitable setting characteristic is particularlyimportant (DE 23 19 715 A). There are numerous compounds which aresuitable for this purpose, in particular those which contain hydroxyl orcarboxyl groups, or both, which form the chelating agents. Particularlygood results have been achieved with tartaric acid or citric acid, inparticular in an amount of 5% by weight. Adding the substance in theform of a metal chelate also has the desired effect.

The polyelectrolyte cements contain from 0 to 10, preferably 0 to 5% byweight of a compound of this type, preferably tartaric acid.

Furthermore, the polyelectrolyte cement may include auxiliaries, such asdyes, pigments, X-ray contrasting agents, flow improvers, thixotropicagents, polymer thickeners or stabilizers.

Examples of standard fillers for dental materials are glass and quartzpowder, plastic powder, pyrogenic highly dispersed silicas and mixturesof these components.

Other suitable fillers may include: aluminum oxide, mineral powders,feldspars and kaolin.

These other additives are usually present in the polyelectroyte cementsaccording to the invention in amounts of from 0 to 60% by weight.

The abovementioned fillers may also be rendered hydrophobic by means ofa surface treatment with organosilanes or organosiloxanes or byetherification of hydroxyl groups to form alkoxy groups.

In principle, the glass composition which has been described is alsosuitable for use in monomer-modified cements.

It has proven favorable for the glass to contain from 20 to 70% byweight, preferably from 30 to 60% by weight, of weakly basic oxides.

The cement according to the invention may if appropriate containstrongly basic oxides in an amount in the range from 0 to 25% by weight,preferably in the range from 0 to 10% by weight.

The cement according to the invention preferably has a flexural strengthin the region of at least 25 MPa to 35 Mpa, particularly preferably ofgreater than 45 MPa, measured in accordance with ISO 4049.

The working time of the cement, which is determined using a viscometer,is 1 to 4 min, particularly preferably 2 to 3 min. The hardening time is3 to 10 min, particularly preferably 4 to 8 min.

Preferred compositions of the glasses are given below.

In addition to the abovementioned weakly basic oxides from the scandiumseries, the glasses may also contain oxides from transition groups 4 and5. Also, the aluminum oxide may be partially or completely replaced byboron oxide or gallium oxide. The melting conditions can be positivelyinfluenced by the addition of oxides from the first main group,phosphate, and/or basic oxides from the second main group or ZnO.

The oxides which are separated from one another by “+” in the table,may, according to the invention, also be present just individually. Thecrucial factor is the corresponding proportion by weight which the groupforms in the glass.

TABLE 1 Oxide Proportion Y₂O₃ + La₂O₃ + other 30 to 80% by weight,preferably lanthanide oxides 35 to 60% by weight B₂O₃ + Al₂O₃ + Ga₂O₃  5to 50% by weight, preferably 10 to 40% by weight, particularlypreferably 15 to 35% by weight SiO₂ + GeO₂ + SnO 10 to 50% by weight,preferably 15 to 50% by weight P₂O₅  0 to 15% by weight, preferably  0to 10% by weight, particularly preferably 0 to 2% by weight MgO + CaO +SrO + ZnO + BaO  0 to 10% by weight, preferably  0 to 8% by weight,particularly preferably 0 to 5% by weight Li₂O + Na₂O + K₂O + Rb₂O +Cs₂O  0 to 5% by weight, preferably  0 to 3% by weight, particularlypreferably 0 to 2% by weight TiO₂ + ZrO₂ + HfO₂  0 to 10% by weight,preferably  0 to 4% by weight, V₂O₅ + Nb₂O₅ + Ta₂O₅  0 to 10% by weight,preferably  0 to 4% by weight,

Instead of the “Y₂O₃+La₂O₃+other lanthanide oxides”, it is also possiblefor Sc₂O₃ to be present in an amount of from 20 to 50% by weight,preferably from 20 to 30% by weight. Glass compositions in which Sc₂O₃is present in addition to the above constituent in a relatively smallamount are also included.

In one embodiment, the invention relates to a dental cement comprising:

-   -   a) mineral solid in an amount of from 50 to 90% by weight;    -   b) water in an amount of from 5 to 50% by weight; and    -   c) polyacid in an amount of from 5 to 50% by weight.        Further, the P₂O₅ of Table 1 may be provided in an amount of        from 0 to 18% by weight.

The invention is explained in more detail below with reference to anumber of examples.

None of the glasses described in the examples was treated with aninorganic acid leading to a reduction in the number of reactive ions atthe surface of the glasses (acid wash) before being reacted with apolyacid.

Production of the Glass:

Glasses of the following oxidic compositions (in % by weight) weremelted at temperatures in the range from 1300 to 1600° C. over a periodof 30 min to 5 h. With the exception of Comparative Example 4, thefluorine content in the starting batch was 12 to 14% by weight.

In Comparative Example 4, a glass was melted in accordance with DE 20 65824 A1 using the following composition:

9.5 g of SiO₂, 10.0 g of Al₂O₃, 7.6 g of Na₃AlF₆, 9.4 g of LaF₃, 7.3 gof AlPO₄. The table gives the oxidic composition used in these examples.

TABLE 2 1 2 3 4 5 6 7 8 9 C1 C2 C3 C4 C5 C6 C7 SiO₂ 20 19 20 17 32 27 1321 19 20 18 46 23 17 26 29 Sc₂O₃ Y₂O₃ 36 58 20 41 50 46 49 48 30 La₂O₃48 63 20 34 22.5 23 CaO 7 16 47 3 16 SrO 17 Al₂O₃ 44 26 22 20 28 32 3728 26 29 34 35 36 26 30 27 P₂O₅ 6 10 5 ZrO2 5 Na₂O 1 1 1 2 8.5 6 1 Li2O13Milling

60 to 80 g of the glass granules obtained were dry-milled for 40 to 50min a vibratory agate mill (produced by Siebtechnik, milling vessel 100ml, 910 rpm). The glass powders obtained had a mean grain size in therange from 3 to 6 μm with a specific surface area of from 1.8 to 2.5m²/g.

EXAMPLE 6

Glass Example 6 was additionally wet-milled using a stirred ball mill.An aluminum oxide vessel (500 ml) was filled with 50 g of glass powder,200 ml H₂O and 100 g of zirconia balls (D=0.8 mm) and milling wascarried out for 6 h using a perforated zirconia disk. The result was amean grain size of 1.5 μm and a specific surface area of 10.5 m².

Cements

The cements were produced as a result of the glass powders obtainedbeing mixed with polyacids. In this step, an approximately 45% strengthpolyacrylic acid (molecular weight 20,000 to 30,000), an approximately45% strength polyacrylomaleic acid (molecular weight approx. 40,000 to60,000) and an approximately 55% strength polyvinylphosphonic acid(molecular weight approximately 20,000) were used.

The setting was determined firstly in accordance with ISO 9917 andsecondly using the viscometer described in EP 0 023 013 A1. In allcases, the test assembly ensured that the temperature of the specimenswas controlled at 28° C. Flexural strengths were determined using thethree-point bending test on 2×2×25 mm cement specimens in accordancewith ISO 4049.

Results:

Cement 1:

Glass 1 was mixed both with a polyacrylic acid and a polyacrylomaleicacid with a P:F of 3:1.

TABLE 3 Polyacrylomaleic Polyacrylic acid acid Viscometer  3:30  3:50(working time) Viscometer  9:10  9:00 (hardening time) ISO 9117  8:30 7:30 Flexural strength 39.4 31.8 [Mpa]Cement 6:

Glass 6 was reacted with polyacrylic acid (45% strength) with a P:F of2.0:1.

TABLE 4 Stirred-ball Dry milling milling Viscometer  5:00  2:10 (workingtime) Viscometer 12:00  7:45 (hardening time) ISO 9117 10:30  4:00Flexural strength 27.9 MPa 41.5 MPaGlass C6:

The glass, in one case untreated and in one case after conditioning for6 hours at 400° C. in a circulating air oven (produced by Heraeus), wasreacted with polyacrylic acid.

TABLE 5 untreated conditioned Viscometer not determinable  1:50 (workingtime) Viscometer  5:20 (hardening time) ISO 9117 not determinable  5:00Flexural strength not determinable 37.4 MPaFurther Cement Examples:

TABLE 6 Glass 2 3 4 5 7 8 9 C1 C2 C3 C4 C5 C7 P:F 3:1  3:1  3:1  3:1 3.5:1   4:1  4:1  3:1   3:1  3:1  3:1  4:1  4:1 Viscometer 1:30 2:502:40 3:20  4:00 3:50 2:50 0:45 <1:0 <1:0 <1:0 <1:0 <1:0 (working time)Viscometer 3:50 8:20 5:20 7:40  9:10 8:50 6:45 1:30 <1:0 <1:0 <1:0 <1:0<1:0 (hardening time) ISO 9917 4:00 7:15 5:00  8:30 7:40 6:00 1:00 <1:0<1:0 <1:0 <1:0 <1:0 Three- 37.4 41.6 34.8 35.6 32.9 43.9 — — — — — —point flexural strength

The setting times determined for the cements obtained in Examples 1 to 9are all within the preferred range, with the exception of Glass 6, whichwas only dry-milled.

The cement in accordance with Comparative Example 1 sets too quickly,presumably on account of the high Ca content. With the cements accordingto Comparative Examples 2 and 3, measurement was no longer possible, onaccount of setting taking place too quickly.

With the measurements using the viscometer, the first time correspondsto the working time and the second time corresponds to the hardeningtime. The times given are in minutes. The P:F ratio is given as a weightratio.

The cements according to the invention are usually marketed packaged invessels. In this context, it should be ensured that the individualcomponents of the cement are in a form which is such that there is noundesirable reaction before they arrive at their intended use. Thevessels usually have at least two chambers which are separated from oneanother. Examples of suitable vessels are described in WO 00/30953 A orEP 0 783 872 A.

Suitable vessels are mixing capsules and closeable box-like hollowbodies, such as screw-capped jars. In one embodiment, the vessel has atleast two compartments. In such an arrangement, the free-flowingconstituents may be separated from the solid constituents of the cement.Depending on the particular application, the cements may also bepackaged in capsules.

1. A dental cement comprising a dental glass comprising: OxideProportion a member selected from the group [[30]] 35 to 60% byconsisting of Y₂O₃, weight La₂O₃, Gd₂O₃, Yb₂O₃, and Lu₂O₃ or 20 to 50%by weight Sc₂O₃ by itself Al₂O₃ 15 to 40% by weight SiO₂ 15 to 50% byweight P₂O₅ 0 to 2% by weight at least one of MgO, CaO, SrO, ZnO, and 0to 8% by weight BaO at least one of Li₂O, Na₂O, K₂O, Rb₂O, 0 to 2% byweight and Cs₂O at least one of TiO₂, ZrO₂, and HfO₂ 0 to 4% by weightat least one of V₂O₅, Nb₂O₅, and 0 to 4% by weight Ta₂O₅


2. The dental cement of claim 1, further comprising: A) mineral solid inan amount of 50 to 90% by weight, B) water in an amount from 5 to 50% byweight and C) polyacid in an amount from 5 to 50% by weight, wherein themineral solid comprises the dental glass.
 3. The dental cement asclaimed in claim 1, wherein the dental material comprises athree-component system.
 4. The dental cement as claimed in claim 1,wherein fluorine replaces from 0 to 25% by weight of the oxygen in thedental glass.
 5. The dental cement as claimed in claim 1, wherein thedental glass is in powder form with a specific BET surface area of 1 to15 m²/g.
 6. The dental cement as claimed in claim 1, wherein the dentalglass has a mean grain size in a range from 0.01 to 10 μm.
 7. The dentalcement as claimed in claim 1, wherein the surface of the dental glasshas not been washed with acid, surface coated or conditioned in order toadjust the setting time.
 8. The dental cement as claimed in claim 1,further comprising at least one filler from 0 to 60% by weight incomponent A).
 9. The dental cement as claimed in claim 8, wherein saidat least one filler is selected from the group consisting of quartz,glasses, aluminum oxide, mineral powders, feldspars, kaolin, and plasticpowder.
 10. The dental cement as claimed in claim 2, wherein the dentalcement has a flexural strength of at least 25 MPa when determined inaccordance with ISO
 4049. 11. A method of producing a dental cement asdescribed in claim 2, wherein the surface of the dental glass has notbeen washed with acid, surface coated, or conditioned, wherein thedental cement is a polyelectrolyte cement and wherein the components ofthe dental glass are melted to form a dental glass, comprising the stepof mixing the mineral solid, water and polyacid to form the dentalcement.
 12. A process for producing the dental cement according to claim1, comprising reacting a polyacid with weakly basic reacting oxidespresent in the glass where the glass has not been surface treated. 13.The process as claimed in claim 12, wherein the dental cement is apolyelectrolyte cement.
 14. A vessel, comprising a dental cement,wherein the dental cement comprises a dental glass comprising: OxideProportion a member selected from the group consisting of 35 to 60% byweight Y₂O₃, La₂O₃, Gd₂O₃, Yb₂O₃, and Lu₂O₃ or 20 to 50% by weight Sc₂O₃by itself Al₂O₃ 15 to 40% by weight SiO₂ 15 to 50% by weight P₂O₅ 0 to2% by weight at least one of MgO, CaO, SrO, ZnO, and BaO 0 to 8% byweight at least one of Li₂O, Na₂O, K₂O, Rb₂O, and 0 to 2% by weight Cs₂Oat least one of TiO₂, ZrO₂, and HfO₂ 0 to 4% by weight at least one ofV₂O₅, Nb₂O₅, and Ta₂O₅ 0 to 4% by weight

and comprising A) mineral solid in an amount of 50 to 90% by weight, B)water in an amount from 5 to 50% by weight and C) polyacid in an amountfrom 5 to 50% by weight, wherein the mineral solid comprises the dentalglass, and additional constituents; wherein the vessel comprises atleast two compartments; and wherein free-flowing constituents areseparated from solid constituents.
 15. A vessel, comprising a dentalcement according to claim 1, wherein the vessel comprises at least twochambers wherein components capable of flowing are separated from thesolid components in the at least two chambers.
 16. The vessel as claimedin claim 15, wherein the vessel is in the form of a mixing capsule.